Rotary drill bits are often used to drill oil and gas wells, geothermal wells, and water wells. One type of rotary drill bit is a fixed-cutter drill bit having a bit body comprising matrix and reinforcement materials, commonly referred to as a matrix drill bit or an infiltrated metal-matrix composite (MMC) drill bit. MMC drill bits are typically manufactured by depositing powder reinforcement materials into a mold cavity and subsequently combining the reinforcement materials at elevated temperatures with a binder material, such as a metallic alloy. The various features of the resulting MMC drill bit, such as blades, cutter pockets, and/or fluid-flow passageways, may be provided by shaping the mold cavity and/or by positioning temporary displacement material within interior portions of the mold cavity. A preformed metal blank or mandrel may be placed within the mold cavity to provide reinforcement for the MMC bit body and to help facilitate attachment of the resulting MMC drill bit to a drill string following fabrication.
The mandrel used in infiltrated MMC drill bits is typically made of a common steel grade material and is weldable to a hardened steel upper shoulder connection or “shank” of the MMC drill bit that facilitates connection of the MMC drill bit to drill string. The mandrel also provides toughness and support/structure to the MMC drill bit as it withstands and transmits the applied forces and torque during drilling operations. During the aforementioned infiltration process, a joint is formed as a braze-like bond between the mandrel and the matrix reinforcement materials to form the head of the MMC drill bit. The integrity of the joint is critical in ensuring that a separation event between the head of the MMC drill bit and the shank does not occur during drilling.